In recent years, in fields relating to graphic decorative printed matter such as vehicle interior device control panels, household electrical appliance labels and designs on tablet device frames and enclosures, demands are increasing for more convenient and low-cost production of printed matter with greater diversity of design and increasingly high definition, having both fine patterns (for example, dot patterns with diameters of about 100 μm, or fine line patterns), and wide-area solid patterns. It is requested to attain higher quality and higher definition of the visibility of printed images that comprise both fine patterns and solid patterns, by improving the sharpness of the image edge sections in solid patterns while also obtaining a satisfactory leveling property.
Moreover, in the fields of black stripe or black matrix printing, as a type of graphics decoration in electric or electronic fields, there is a demand for obtaining a high degree of definition that provides sharpness to the printed images without bleeding or spreading, in addition to stable printing of fine lines, and it is desired to accomplish high definition printing with satisfactory visibility in a single step regardless of the size of the printed area, for cost reduction.
Also recently, with advancing diversity of product shapes, and especially for printed matter printed on thermoplastic resin substrates such as plastic, it has become common to carry out three-dimensional shape molding by post-working such as curving, folding, or vacuum forming or pressure forming.
For this reason, it is desired to accomplish an even greater level of precision of printed matter before shape working, or in other words need for increased high quality and high definition, and there is a strong desire for an ink for screen printing that can produce printed matter having both durability and flexibility in order to follow shape working.
In conventional screen printing, when printing a dot pattern or fine line pattern of approximately 100 μm, printing is usually performed using a high-viscosity screen printing ink of about 10 to 200 Pa·s, with a reduced flow property, but printing of solid patterns with such high-viscosity screen printing inks cannot avoid creation of leveling defects or printing abnormalities in the solid patterns due to the poor flow property, and as a result the visibility of the printed matter is impaired. Furthermore, when a low-viscosity screen printing ink of several Pa·s is used for satisfactory printing of solid patterns, it has been impossible to avoid spreading of ink that may exceed about 50 to 100 μm at the solid pattern image edge sections, or enlargement, spreading or bleeding of fine patterns, that impair the visibility of the printed matter. Thus, screen printing of fine patterns and solid patterns is performed separately with different inks suitably prepared for each, and it has been considered difficult to produce printed matter by screen printing of a single step comprising both the fine patterns and solid patterns mentioned above, as well as, for example, solid patterns with sizes of about 100 mm-square that are adjacent across fine spacings of about 100 μm.
In addition, it has been considered even more difficult to impart performance for shape working to such inks for screen printing that can produce high quality and high-definition printed matter in a single step.
Here, ink jet printing is considered to allow high-precision printing of printed matter comprising both fine patterns and solid patterns in a single step, and many attempts have been made to accomplish high-quality/high-definition printing by ink jet printing, however, since ink jet printing involves spraying ink droplets from a head nozzle with a diameter of about 30 μm, which spread out to about 50 μm at minimum when the droplets impact with the object being printed, it has been the case that such printing lacks sharp linearity especially at image edge sections.
Furthermore, inks for ink jet printing is requested to have low viscosity of about a few mPa·s due to the printing mechanism that injects droplets as described above, while major restrictions on the materials remain for using such inks, and fatal difficulties regarding the materials remain for imparting suitability for shape processing with excellent durability and flexibility.
In addition, offset printing is estimated to be a printing system that allows creation of high-quality/high-definition printed matter. However, since the structure of the printing plate is mesh-state, resulting in the printed images that are aggregated prints of halftone dots, it is impossible to avoid a lack of sharp linearity at image edge sections as is the case of ink jet printing. In addition, the printing film thickness is narrow at about 1 to 2 μm, and when compared with screen printed matter, they are inferior to screen printed matter in terms of high film thickness, high durability, high weather resistance, high chemical resistance, strong adhesion onto a variety of objects to be printed and high functionality, as well as suitability for shape working, and so they are unsuitable for creation of printed matter with curves, folds and shape working, for which greater durability and functionality are desired for designs on vehicle interior device control panels, household electrical appliance display panels, tablet terminal frames and packages, and black stripes or black matrices for light modulation in electrical and electronic parts.
Prior Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2010-047716) and Prior Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2010-047649) each disclose a conductive ink composition and conductive coating film for screen printing that can form high-definition patterns, but techniques relating to the flow property of ink for printing with both fine patterns and solid patterns have not been pursued, and so while fine patterns can be obtained with satisfactory printing precision, in the case of solid patterns, the leveling property is poor and printing abnormalities are generated. Furthermore, the technical scope of Prior Patent Document 1 is restricted to printing of fine patterns with the conductive ink composition, and it does not disclose technology relating to an ink composition for screen printing that is suitable for shape working and is printed with high precision onto thermoplastic resin substrates.
In addition, in Prior Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2003-238876) and Prior Patent Document 4 (Japanese Unexamined Patent Application Publication No. 2003-294930), ink compositions for screen printing allowing formation of high-definition patterns are disclosed, and similar to Prior Patent Document 1, technology for highly precise printing of fine patterns is disclosed, but following technologies are not disclosed:
technology relating to ink compositions for simultaneous printing of fine patterns and solid patterns in a single step, and technology relating to an ink composition for screen printing that is suitable for shape working and is printed with high precision onto thermoplastic resin substrates.